Rock & mineral identification guide
A plain-English guide to the minerals collectors find most often. Each page covers what the mineral is, how to tell it apart from look-alikes, its key properties, and where it turns up. Found something you can't place? minShelf identifies it from a photo and lets other collectors confirm the answer.
- AgateMohs 6.5–7
Silicate (chalcedony)
Agate is a banded form of chalcedony (microcrystalline quartz), famous for its concentric colour bands and popular with rock tumblers and cutters.
- AmethystMohs 7
Silicate (quartz variety)
Amethyst is the purple variety of quartz, coloured by trace iron and natural irradiation, and one of the most popular collectable gemstones.
- AzuriteMohs 3.5–4
Carbonate
Azurite is a deep-blue copper carbonate that forms alongside malachite in weathered copper deposits and often alters to it over time.
- BariteMohs 3–3.5
Sulfate
Barite is barium sulfate, notable for being surprisingly heavy for a pale, non-metallic mineral, and for forming rosette “desert roses”.
- BerylMohs 7.5–8
Silicate
Beryl is a beryllium silicate whose gem varieties include emerald (green), aquamarine (blue) and morganite (pink), forming six-sided prisms.
- CalciteMohs 3
Carbonate
Calcite is calcium carbonate, a very common mineral that fizzes in acid, cleaves into rhombs and shows striking double refraction in clear crystals.
- CelestineMohs 3–3.5
Sulfate
Celestine is strontium sulfate, loved for its delicate sky-blue crystals that famously line the insides of large geodes.
- ChalcopyriteMohs 3.5–4
Sulfide
Chalcopyrite is a copper iron sulfide and the most important ore of copper, recognisable by its brassy colour and peacock iridescence.
- CitrineMohs 7
Silicate (quartz variety)
Citrine is the yellow-to-golden variety of quartz; most on the market is heat-treated amethyst, while natural citrine is uncommon.
- CopperMohs 2.5–3
Native element
Native copper is the pure metal occurring naturally, a red, malleable element that forms branching, wire-like and sheet-like masses.
- CorundumMohs 9
Oxide
Corundum is aluminium oxide and the second-hardest natural mineral; its red gem variety is ruby and all other colours are sapphire.
- FeldsparMohs 6
Silicate
Feldspar is a group of aluminosilicate minerals that make up the majority of the Earth’s crust, including orthoclase, labradorite and moonstone.
- FluoriteMohs 4
Halide
Fluorite is calcium fluoride, famous for glassy cubic crystals in every colour, perfect octahedral cleavage and often glowing under UV light.
- GalenaMohs 2.5
Sulfide
Galena is lead sulfide, the principal ore of lead, instantly known by its bright metallic cubes, perfect cubic cleavage and great weight.
- GarnetMohs 6.5–7.5
Silicate
Garnet is a group of hard silicate minerals that form distinctive many-sided crystals, most often deep red, and used as both gems and abrasives.
- GypsumMohs 2
Sulfate
Gypsum is a soft, hydrated calcium sulfate that you can scratch with a fingernail; its clear variety, selenite, forms giant glassy crystals.
- HaliteMohs 2–2.5
Halide
Halite is natural rock salt (sodium chloride), forming clear cubic crystals with perfect cubic cleavage and an unmistakable salty taste.
- HematiteMohs 5–6
Oxide
Hematite is iron oxide and the main ore of iron, identified by its diagnostic reddish-brown streak no matter what colour the specimen is.
- JasperMohs 6.5–7
Silicate (chalcedony)
Jasper is an opaque, iron-rich variety of chalcedony in earthy reds, yellows and browns, prized for its patterns when cut and polished.
- MagnetiteMohs 5.5–6.5
Oxide
Magnetite is a black iron oxide and the most magnetic natural mineral, often forming octahedral crystals that attract a magnet.
- MalachiteMohs 3.5–4
Carbonate
Malachite is a green copper carbonate famous for its swirling light-and-dark green bands, used as both a gemstone and a copper ore.
- MicaMohs 2–2.5
Silicate
Mica is a group of sheet silicates that split into thin, flexible, transparent flakes; muscovite is silvery and biotite is dark brown-black.
- ObsidianMohs 5–5.5
Mineraloid (volcanic glass)
Obsidian is natural volcanic glass formed when lava cools too fast to crystallise, prized for its glassy black shine and razor-sharp edges.
- OpalMohs 5.5–6.5
Mineraloid (hydrated silica)
Opal is a hydrated form of silica famous for its “play-of-colour”, flashing rainbow hues, though common opal is solid-coloured.
- PyriteMohs 6–6.5
Sulfide
Pyrite, or “fool’s gold”, is a brassy iron sulfide that forms striking cubes and is famously mistaken for gold.
- QuartzMohs 7
Silicate
Quartz is the most common mineral in the Earth’s crust, a hard, glassy silicon dioxide that forms six-sided crystals in almost every colour.
- RhodochrositeMohs 3.5–4
Carbonate
Rhodochrosite is a rose-pink manganese carbonate, loved for its banded stalactitic slices and, rarely, gem-quality red crystals.
- SmithsoniteMohs 4–4.5
Carbonate
Smithsonite is a zinc carbonate, prized by collectors for its smooth, botryoidal crusts in soft blue-green, pink and lavender.
- StibniteMohs 2
Sulfide
Stibnite is antimony sulfide, forming dramatic bundles of long, bladed, steel-grey metallic crystals sought after by collectors.
- SulfurMohs 1.5–2.5
Native element
Native sulfur is the pure element, a soft, bright-yellow mineral that forms around volcanic vents and hot springs and burns with a blue flame.
- TopazMohs 8
Silicate
Topaz is an aluminium silicate of hardness 8, forming glassy prismatic crystals with one perfect cleavage, in colourless, blue, golden and pink.
- TourmalineMohs 7–7.5
Silicate (borosilicate)
Tourmaline is a borosilicate that forms long striated crystals with a rounded-triangle cross-section, ranging from common black schorl to gem multicolours.
- TurquoiseMohs 5–6
Phosphate
Turquoise is a blue-to-green copper aluminium phosphate, one of the oldest gemstones, usually found as opaque veins and nodules.